This invention is concerned with a device for loosening sub-soil. There are known a number of devices which by means of tools pierce openings into the soil either for the purpose of making grooves for putting in seeds or for the ventilation and/or drainage of the soil etc. Especially for the latter-mentioned purpose the opening produced on the surface of the soil by piercing in the tool and remaining after its removal is to stay small whereas in the deeper area of the soil a more extensive movement of the tool is to be produced transversely to the piercing or digging direction.
It is basically known to pivotably support such piercing tools on a controllable tool carrier on a vertical plane extending in the travelling direction and to move them under the action of spring force against a stop which ensures that the piercing tool prior to being pierced into the soil has a certain orientation thereto which at least approximately agrees particularly with the pressure load direction at the time of penetrating into the soil. The piercing of the tools into the soil takes place with the device being moved in the travelling direction by which travelling movement the tool, which has penetrated the soil, is pivoted in a certain manner, however, not to such an extent that any tearing-up movement takes place on the surface of soil on removing the tool. The small displacement in the soil out of the orientation position predetermined by the stop the tool carries out against the force of the above-mentioned spring. After the tool has left the soil it is again moved under the force of the said spring against the stop and thereby pivoted towards the orientation direction provided for the repeated penetration of the soil. The operation of such tools or arrays of tools takes place in a manner known per se with the aid of a crank mechanism which is operated in the course of the travelling movement corresponding to the desired density of penetration.